Laser with combined q-switch and synchronized cavity dump circuit

ABSTRACT

A laser employing a single modulator in the form of a Pockels cell in the laser cavity and a polarizer. The polarizer in the cavity passes radiation having one polarization direction coming from one direction and diverts radiation having another polarization direction into an absorber. The polarizer passes radiation having one polarization direction coming from an opposite direction and diverts radiation having the other polarization direction into an output path. The modulator in the cavity rotates the polarization direction of radiation to establish the other polarization direction when energized and permits passage of radiation when it is deenergized. A high voltage electrical waveform generator circuit is provided which generates a voltage waveform having a positive DC voltage leading edge and a negative DC voltage trailing edge to the modulator. A gas trigger tube is provided in the circuit which generates a positive DC voltage leading edge in its plate circuit when it is independently triggered by a trigger signal. Another gas trigger tube generates a positive voltage when it is triggered by another trigger signal from a photodiode positioned to intercept radiation leaking from laser cavity. A coupling circuit which couples the plate circuits of the trigger tubes includes a capacitor which converts the positive voltage generated by the other trigger tube into the negative DC voltage trailing edge of the voltage waveform. The coupling circuit may also include a differentiator which allows the voltage levels on the trigger tube plates to be independently varied without affecting each other.

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' SEARCH ROOM [72] Inventor Ronald P.1Hilberg ABSTRACT: A laseremploying a single modulator in the Redondo Beach, Calif.

form of a Pockels cell in the laser cavity and a polarizer. The

[2l 1 Appl- N 76 polarizer in the cavity passes radiation having onepolarization [22] Fil d N 1967 direction coming from one direction anddiverts radiation havl l patfifmed y 4, 1971 ing another polarizationdirection into an absorber. The

[73] Asslgn R Y polarizer passes radiation having one polarizationdirection Redomlo Beach, Calif.

coming from an opposite direction and diverts radiation having the otherpolarization direction into an output path. The modulator in the cavityrotates the polarization direction of radiation to establish the otherpolarization direction when energized and permits passage of radiationwhen it is deenergized. A high voltage electrical waveform generatorcircuit is [54] LASER WITH COMBINED Q-SWITCI-I AND SYNCHRONIZED CAVITYDUMP CIRCUIT 3 Claims, 14 Drawing Figs.

provided which generates a voltage waveform having a posil52] US. Cltive D C Voltage leading g and a negative C voiltagqtraib 51 rm. ClI-IOls 3/00 P edge 9 mOdulato" A 8? tube f h 50 Field of Search331/94.5- 9 whlch Posmve DC VOIFage 'eadmg g 328/91 332/751 its platecircuit when it 15 independently triggered by a trigger signal. Anothergas trigger tube generates a positive voltage [56] References Cit d whenit is triggered by another trigger signal from a UNITED STATES PATENTSphotodiode t'zsitiomled to intercept fradiatipn lgakirltg from t asercavity. coup mg circuit w to coup es t e p ate cir- :Lig: cuits of thetrigger tubes includes a capacitor which converts the positive voltagegenerated by the other trigger tube into e DELAYED the negative DCvoltage trailing edge of the voltage waveform. The coupling circuit mayalso include a differentiator which allows the voltage levels on thetrigger tube plates to be independently varied without affecting eachother.

TRIGGER FLASH LAMP 3s GENERATOR DRIVER 3 SIGNAL Q SWITCH 22 DELAY ANDDUMP .CIRCUIT CIRCUW 38 g PATENTEBMAY 41971 5 I 3577,09?

' sum 1 or 3 l fl/ 2 30 34/ TRIGGER FLASH LAMP as e GENERATOR DRWER 3 8DELAYED SICgNAL Q- SWITCH 22 DELAY AND DUMP CIRCUIT POCKELS I/CELL Cc.40pf k Q-SWITCH ACTIVATING PULSE e,

RADIATION ENERGY INSIDE LASER I CAVITY tq "0 1d 1 Ronald F? HilbergINVENTOR.

BY I AGENT =1 Fig.4o

= Fiq.4b

SHEET 2 OF 3 H Fig.4c

Fig.4d

Fig-4e d Fig.7

Ronald I? Hilbirg 5 AGENT Trumlom l L l Transient VOLTAGE 0N ANODE 0F T4T PATENT-EUMAY 4|97| 0-SWITCH ACTIVATING PULSE 6 0 PULSE e -Fnom PHOTODIODE t VOLTAGE e ow f POCKELS CELL Fig. 5

VOLTAGE e VOLTAGE as UN mom-2 OF T2 PATENTEDHAY 4|97| 3577,09?

SHEET 3 OF 3 QSWITCH PULSE soon QSW|TCH ACTIVATING I PULSE e L 1 Fig 80PULSE e FROM PHOTO-DIODE A v 1 1 FlgBb VOLTAGE e ON V POCKELS CELL tFig-8c OF T3 1 ig-8d Ronald P Hilberg INVENTOR AGENT LASER WITH COMBINEDQ-SWITCII AND SYNCIIRONIZED CAVITY DUMP CIRCUIT BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally tolaser apparatus and more particularly to laser apparatus havingactuating circuitry for such apparatus which generates an actuatingsignal having combined Q-switching and synchronized cavity dumpingsignal portions to a single modulator such as a Pockels cell employed inthe laser.

2. Description of the Prior Art In US. Pat. application Ser. No.625,549, filed Mar. 23, 1967, and entitled "Lasers Incorporating TimeVariable Reflectivity," there is generally provided laser apparatus inwhich there is time variable reflectivity of the laser cavity during thelasing process. The time variable reflectivity relates to the variationof the reflectivity in the cavity during the power buildup prior tolasing and during lasing by varying the voltage at predetermined timesto a polarity rotating means within the cavity and which acts topartially or totally effectively remove the reflectivity of one of thesubstantially 100 percent mirrors at the ends of the cavity. In theabove-mentioned application a Q-switching operation is followed by acavity-dumping operation. The sequence of events involved is to raisethe excited atom population to the desired level while holding theradiation loss in the cavity high enough to prevent lasing, switch theloss in the cavity to a low value, thus allowing the optical energy inthe cavity to build up to a maximum value, and to switch out the energystored in the cavity. Successful operation of such apparatus depends onits ability to open the time variable mirror at the peak of the energypulse. One embodiment of such apparatus employs a pair of modulatorssuch as Kerr cells and active element actuating circuitry providingseparate signals to the Kerr cells for Q-switching and synchronizedcavity dumping.

Another US. application Ser. No. 686,267, filed Nov. 28, 1967, entitledSelf Synchronized Laser Apparatus and Method, reveals and describeslaser apparatus which also employs a pair of modulators with passiveelement actuating circuitry which generates separate signals forQ-switching and synchronized cavity dumping.

SUMMARY or THE INVENTION Laser apparatus wherein means is provideddefining a laser cavity, and a source of radiation within the cavity.Polarizer means is situated in the cavity for passing radiation havingone polarization direction coming from one direction and divertingradiation having another polarization direction into an absorber. Thepolarizer means passes radiation having the one polarization directioncoming from an opposite direction and diverts radiation having the otherpolarization direction into an output path. There is also provided inthe cavity a single cell for rotating the polarization direction ofradiation to establish the other polarization direction when energizedand for permitting passage of radiation when deenergized. A circuitmeans connected to the cell is provided for sequentially energizing,deenergizing, and energizing the cell.

The present invention has advantages in that it provides laser apparatusemploying a single modulator such as a Pockels cell and actuatingcircuitry which generates a single voltage waveform signal to the cellfor both Q-switching and cavity dumping. The voltage waveform providesboth a switching portion and a synchronized dumping of the cavity energyportion. More specifically, the apparatus provides circuitry whichgenerates a single voltage waveform having the followingcharacteristics:

1. Before Oswitching takes place it has a;6 Kv. DC portion suitable forbiasing the Pockels cell sufficient to prevent lasing in the cavity.

2. When Q-switching is initiated the '+6Kv. DC biasing volt- 3. Uponinitiation of cavity dumping, the bias DC voltage goes to a 6 Kv.one-fourth wave retardation voltage portion within 3 nanoseconds, and adelay time of less than 30 nanoseconds. Another advantage is that the DCretardation bias voltage portion of the waveform can bepreciselyadjusted such that if the excited atom population excess thedesired value due to overpumping, the population will automaticallydeplete itself back to the desired value by the ordinary lasing process.This is a very important advantage involving a safety feature whichguards against creating of the condition whereby the power in the lasercavity due to Q-switching becomes excessive. Another advantage is thatsmall and inexpensive components can be utilized in the practice of theinvention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic showing, partlyin block diagram, of the laser apparatus incorporating the presentinvention;

FIG. 2 shows in schematic form thedetails of the preferred embodiment ofthe Q-switch and dump circuit of FIG. 1;

FIG. 3 shows a graph relating radiation energy occurring inside thelaser cavity of FIG. 1 and time which is helpful to the understanding ofthe present invention;

FIGS. 4a4e show graphs of voltages to be found in various parts of thecircuit of FIG. 2;

. FIG. 5 shows in schematic form the details of a modification of thecircuit of FIG. 2;

FIG. 6 shows in schematic form the details of another em bodiment of theQ-switch and dump circuit of FIG. 1;

FIG. 7 shows a graphof a voltage occurring in the circuit of FIG. 6; and7 FIGS. 8a8d show graphs of voltages to be found in various parts of amodification of the apparatus of FIG. 6 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FlG. 1 there isshown a laser apparatus 10 of the present invention for producingcoherent radiation according to time variable reflectivity principles.The laser 10 generally comprises a pair of mirrors 14 and 16 defining aresonant cavity. Positioned within the cavity is a laser rod 17, apolarizer 18, and an electro-optic member 20. A flash lamp 21 isprovided for pumping the rod 17. Positioned outside the cavity is anelectric circuit generally designated by the numeral 22 for actuatingthe lamp 21 and the electro-optic member 20.

The rod 17 can be comprised of neodymium. The opposite ends of the rod17 are directed toward the reflecting surfaces of the mirrors 14 and 16with the rod having its longitudinal axis perpendicular to the mirrors.For regeneration of the excited atoms in the laser rod 17, the outputbeam therefrom is confined along its longitudinal axis and is polarizedin a direction normal to the axis of the rod 17. The direction ofpolarization of the laser radiation is determined by the orientation ofthe polarizer 18. For Glan polarizer 18 shown in FlG. 1, the directionof the polarization of the laser radiation is horizontal, or in theplane of the drawing. Adjacent to the rod is positioned the flash lamp21 which can be a xenon flash tube, for example.

The mirrors 14 and 16 are positioned parallel to each other and aresubstantially percent reflective. The polarizer 18 and the electro-opticmember 20 are in axial alignment with the laser rod 17. The laser cavitybetween the mirrors 14 and 16 has a length of approximately 24 inches.All of the flat surfaces within the cavity except the mirrors can beantireflection coated.

The polarizer 18 acts to send radiation in a particular direction,depending on the polarity direction of the radiation. The polarizer 18may be a Glan polarizer and fashioned from a material such as calcite.The polarizer has a shield 30 on the side which prevents the emission oflight from that side.

Radiation which is coming toward the polarizer I8 from the left or inother words from the direction of the laser rod 17,

passes undiverted through the polarizer if such radiation ishorizontally polarized, but is diverted into the absorber 30 if suchradiation is vertically polarized. Radiation which is approaching thepolarizer 10 from the right, or in other words from the direction of themirror 16, also passes undeviated through the polarizer 1% if suchradiation is horizontally polarized, but is diverted in the outputdirection 32 if such radiation is vertically polarized.

The electro-optic member 20 acts as a polarization rotator, whenenergized, and is effective to rotate the direction of the polarizationof the polarized radiation through predetermined angles depending uponthe voltage applied. When it is not energized it does not affect thepolarity of the laser radiation. The electro optic member 20 may be aPockels cell and is in axial alignment with both the rod 17 and thepolarizer IS. The Pockels cell 20 may be of the type commerciallydesignated as EOA-4I5B and which can be activated with a voltage pulseof 6,000 volts at L06 microns. Thus, when there is no voltage on thePockels cell 20 an undeviated transmission of laser radiation takesplace through the Pockels cell 20 and the polarizer I18. When thePockels cell 20 is energized, the path of the polarized laser radiationis controlled by the rotation at the Pockels cell 20 such that it isdiverted by polarizer IS in the output direction 32. The Pockels cell 20may be energized with either a positive voltage or a negative voltage,and the effect of the Pockels cell 20 on the polarized laser radiationis the same. In other words, the laser radiation can be diverted bypolarizer Iii in the output direction 32 by the application of either apositive 6,000 volts or a negative 6,000 volts to the Pockels cell 20.

In accordance with the time variable reflectivity principles of thisinvention there occurs a high cavity loss interval when the Pockels cell20 is positively biased, a laser radiation buildup interval when thePockels cell 20 is unbiased, and an output or cavity dumping intervalwith the Pockels cell 20 negatively biased. 1 I

The circuit 22 consists of a trigger generator 3 2 which provides anoutput signal e' for actuating a flash lamp driver 36 to pump the lamp2.1 to excite the atoms in rod I7. A delay circuit 38 connected to thetrigger generator 3d and a Pockels cell Q-switch and cavity dump circuitd serves to delay the signal 0, a predetermined time so as to providethe circuit 40 with a delayed signal 6,. A photodiode d2 positionedoutside the laser serves to monitor the light output leaking throughmirror M and generates a signal e, to the circuit at). The circuit it)is responsive to the delayed signal 2, and the signal e, and isconnected to the Pockels cell 20 so as to provide a bias signal a in itsoutput thereto.

Reference is now made to FIG. 2 wherein there is shown the details ofthe circuit 40 of FIG. II which is capable of generating the voltagewaveform a, needed to accomplish the necessary sequence of events,namely a high cavity loss interval, a laser radiation buildup intervaland a cavity dumping interval. A trigger gas tube TI is adapted to haveits control grid 48 connected to the delay circuit 38 for actuationthereby with the delayed signal 42,. A resistor i9 connects the grid 48to ground. The anode 50 of tube T1 is connected through a resistor 52 toa source (not shown) of variable DC voltage V,. The tube Tll may be aKrytron cold cathode switch tube type Kid-22. The anode '0 of tube TI isalso connected through a resistor 58 and coaxial cable so to the Pockelscell 20. A capacitor 62 along with the resistor 6d serves to form adifferentiator circuit at, which is AC coupled by capacitor 68 to theplate 70 of a gas switch tube T2. The tube T2 can be a type I(N-6BKrytron tube which is commercially available. The anode 70 is connectedthrough a resistor 72 to a variable DC voltage V supply source (notshown). A keep-alive grid 74 of tube T2 is likewise connected through aresistor 76 to the source of variable DC voltage V,. The control grid 78of tube T2 is connected through a capacitor 00 to the photodiode 12. Aresistor 82, connected at one end to the side of the capacitor 00 whichis connected to photodiode 42, is connected at the other end to a source(not shown) providing a 4 Kv. DC

voltage. A resistor 83 connected at one end to the control grid 79 isconnected at the other end to ground.

Operation of the laser apparatus of this invention can best be describedwith reference to FIGS. 1, 2, 3, and 4. Initially the voltages V, and V,are each independently adjusted to 6 I(v., for example, and are appliedto the plates of tubes T1 and T2, respectively. The application of avoltage V, on the plate of tube Tll provides a positive DC voltage onthe Pockels cell which causes rotation of the polarization of radiationemanating from the rod 17 such that a high energy loss condition isestablished within the laser cavity. In this condition laser radiationemanating from the rod 17 is diverted by polarizer 10 either into theabsorber 30 or in the output direction 32, depending on the polarizationof the radiation. Next, at time t,, the trigger generator 3 5 isactuated to provide the signal 2, which causes the flash lamp driver 36to energize the lamp 21 to start nonregenerative pumping or irradiatingof the atoms in the rod 17. The number of excited atoms in the rod 17reaches a maximum within a few hundred microseconds. The signal 2, isdelayed by the delay circuit 33 for a time (t,,l,,) which is equal tothe time it takes for the number of excited atoms to reach a maximum,and at time t as shown in FIG. 4a, the delayed signal e, is applied tothe grid 48 of tube TI causing tube T1 to conduct heavily, and thereforecausing the anode 50 thereof to short to ground and the voltage 0,, onthe Pockels cell 20 also to go quickly from V, to zero. With voltage V,thus removed from the plate 50 of tube TI and the Pockels cell 20, anundeviated transmission of radiation takes place through the polarizer18 and the Pockels cell to the mirrors l4 and 16 such that lasing beginsto take place within the cavity, and the radiation energy starts tobuildup within a frequency range including the characteristic frequencyof the lasing atoms in the rod 21.

The change from V, to zero in voltage 2 which occurs at time 1,, isdifferentiated by the differentiator network 66, and thus appears as ashort negative going transient in the voltage e, as shown in FIG. dd. Asimilar negative transient appears in the voltage 2 on the anode of tubeT2 as shown in FIG. 4e. The purpose of the differentiating circuit 66 isto prevent the entire step change in the voltage te from being ACcoupled to the anode of T2, to thus subtract from the voltage level V,,which normally appears on the anode of T2. The use of thedifferentiating circuit (16 thus prevents interaction between thechanges in the hold-off voltage V, and the dumping voltage V,,.

An interval of about nanosecond occurs before the radiation energyreaches a significant level as indicated at 1,, in FIG. 3 after whichthe level rapidly rises to its peak intensity designated at r That is,after time t,,, photons are emitted from the laser rod 21 and make manytraversals within the cavity through the rod 17 and between the mirrorsl4, 16, passing through the Pockels cell 20 and the polarizer 13 withoutdeviation. As the radiation energy builds up between I,, and r, in FIG.3, the population of excited atoms rapidly decreases. The time between1,, and t,, is approximately 200 nanoseconds. The power leaking throughthe mirror 14 builds up at the same rate as the energy within thecavity, and thus the voltage pulse that appears at the output ofphotodiode 42 has the same shape as that of the energy pulse of FIG. 3.This voltage pulse is shown in FIG. 4b and is designated e-,.

The pulse 6 is applied to the trigger grid 78 of tube T2 whereby thetube T2 becomes shorted to ground and the voltage on its plate 70 dropsto zero as shown in FIG. 4e, and the voltages e, and e, develop negativegoing portions as shown in the FIG. dc and id, respectively. There is aninterval delay in the tube T2, such that a short interval of timeelapscs between the application of a triggering voltage to its grid 78and the time at which the tube T2 becomes conducting. This intervaldelay can be changed by changing the keep-alive current applied to thegrid 74. In the operation of this embodiment of the invention the amountof keep-alive current and the amplitude of the signal e applied to thegrid 78 of tube T2 are adjusted such that tube T2 becomes conducting atthe time t,, when the laser radiation energy within the cavity is at amaximum. With the application of the negative-going portion of the e;voltage to the Pockels cell at time 1,, as shown in FIG. 4c, rotation ofthe polarization of the radiation in the cavity is achieved andtheenergy is caused to follow the path 32 out of the polarizer 18. It willbe appreciated that it is only necessary that the voltage be maintainedat the negative value for a few nanoseconds, since its only function isto cause draining of the laser cavity of radiation.

The circuit of FIG. 2 can be modified to decrease the fall time of thenegative bias voltage portion of the voltage e used to dump the cavityat time In this modification a type KN- .22 tube is substituted for theI(N6B tube utilized in the embodiment of FIG. 2. The KN-22 has a fasterturn on time than the KN-6B, but has a lower voltage capability. Thus,in order to achieve the desired magnitude of the negative bias voltageportion of the voltage 2 the circuit of FIG. 2 is also provided with avoltage doubler in the form of a length of coaxial cable 67 such asRG58, 50 ohm cable which is inserted between the capacitor 68 and thejunction of capacitor 62 and a resistor 69 having an ohmic value of 500,substituted for the resistor 64, as shown in FIG. 5. The length of cable67 should be such as to provide voltage doubling. The operation of thismodified circuit is the same as that of the circuit of FIG. 2 exceptthat a lower voltage V can be applied to the anode of Reference is nowmade to FIG. 6 wherein there is shown the details of still anotherembodiment of the Q-switch and dump circuit of FIG. I. The circuit ofFIG. 6 is somewhat similar to the circuit of FIG. 2 and like numeralsdesignate like parts. In FIG. 6 a triggered spark gap tube T3 and a gasswitch tube T4 with associated components are substituted for the tubeT2 of FIG. 2. The tube T3 can be a commercially available GP- l7A andthe tube T4 can be a KN22. The opposite electrode 84 of the tube T3 isadapted to be connected through a resistor 86 to the source (not shown)of variable DC voltage V The adjacent electrode 88 of the tube T3, isconnected to ground and the trigger probe 90 is connected through aresistor 92, coaxial'cable 94, capacitor 96 to the plate 98 of tube T4.A resistor 100 connects the connecting point between the resistor 92 andcable 94 to ground. The control grid I02 of tube T4 is connected asshown and the keep-alive grid I04 is connected through a resistor I06 toa source (not shown) of DC voltage V A resistor 108 connects the anode98 to the same source (not shown) supplying the DC voltage V The re-Sister 82 is connected to a source (not shown) supplying a 2.5 Kv DCvoltage. The cable 94 serves as a voltage doubler and is long enough toachieve the desired voltage doubling.

Operation of the circuit of FIG. 6 is similar to the operation of thecircuit of FIG. 2 up through the time 1,, and can best be describedhaving reference to FIGS. 3, 4, 6 and '7. The voltage V,, V,, and V;,are initially applied to the tubes Tl, T3, and T4, respectively. Asbefore, the application of voltage V, on the plate of tube Tl provides apositive DC voltage bias on the Pockels cell 20 which causes radiationemanating from the rod 17 to be diverted either into the absorber 30 orin the output direction 32, depending on the polarization of theradiation to establish a high energy loss condition within the lasercavity. At the time 1,, the trigger generator is actuated to provide thesignal e to the lamp driver 36 which energizes the lamp 21 to start thepumping of atoms in the rod. The signal e is delayed for the time (I -tand is then applied to the grid 48 of tube Tl causing it to conduct andthe voltage e on the Pockels cell 20 to go from a voltage V, to zero.With the voltage V removed from tube T1 and the Pockels cell 20 lasingbegins within the cavity as before. The change in voltage e occurring attime 1, appears as the negative going transient in the voltage e.,, andas a similar transient in the voltage a appearing on the electrode 84 oftube T3. The circuit of FIG. 6 can be triggered at a somewhat lowervoltage level from the phototube 42 and has a shorter trigger delay thanthat inherent in the tube T2 of FIG. 2. As the energy in the lasercavity builds up, some of this enerE leaks through the mirror 14 and, asin the embodiment of F 2, energizes the photodlode 42 to produce thecavity dump signal e The pulse a; is applied to the'grid 102 of the tubeT4 whereby the tube T4 becomes shorted to ground and the voltage V;, onthe anode of T4, as shown in FIG. 7, drops to zero producing a negativegoing pulse which is doubled in magnitude by the voltage doubler cable94. This negative going pulse is AC coupled to the trigger probe of tubeT3 which becomes shorted to ground and the voltage on its oppositeelectrode 84 drops to zero as shown in FIG. 4e. This negative goingvoltage is AC coupled back to the Pockels cell 20, and the voltagethereon goes from zero to a negative value, as shown in FIG. 4c.

The circuit of FIG. 6 can be modified to eliminate the differentiatorcircuit 66 therefrom. Operation of such a modified circuit is similar tothe operation of the circuit of FIG. 6 and provides the correspondingvoltage waveforms shown in FIGS. 8a-8d. With this circuit a shorter timeinterval between 0- switching time 1,, and cavity dumping time t,, canbe obtained, since it is not necessary to wait for the differentiatedpulse e of the circuit of FIG. 6 to recover. However, a change in eitherone of the applied voltages V, or V affects both the 0- switching anddumping voltage portion levels applied to the Pockels cell.

It will be obvious to those skilled in the art that many other changesand modifications of the invention may be made without departing fromthe true scope thereof as defined in the appended claims.

Iclaim: v

1. Laser apparatus comprising:

means defining a laser cavity;

laser means in said cavity for emitting radiation;

light polarizer means in said cavity;

cell means in said cavity for changing the polarity of light;

a first trigger gas switch tube having an anode connected to said cellmeans and to a first source of variable DC voltage capable of supplyinga first predetermined voltage at said anode and cell means for changingthe polarization of light within said cavity to establish reducedreflectivity within said cavity, said first tube being responsive to atrigger signal eliminating said first voltage at said anode and cellmeans to deenergize said cell means to establish light amplificationwithin said cavity;

a second trigger gas switch tube having an anode connected to a secondsource of variable DC voltage capable of supplying a secondpredetermined voltage at said anode, said second tube being responsiveto a trigger signal generated by energy leading from said cavity at itspeak amplified value eliminating said second voltage at said second tubeanode; and

capacitor means interconnecting said anodes for providing a voltage tosaid cell means in response to changes in said second predeten'ninedvoltage to change the polarization of light within said cavity and todischarge the light energy at its peak amplified value from said cavity.

2. The laser apparatus of claim 1 further comprising: differentiatorcircuit means in series connection with said capacitor means.

3. The apparatus of claim 2 further comprising: voltage doubling meansin series connection with said capacitor and differentiator means.

2. The laser apparatus of claim 1 further comprising: differentiator circuit means in series connection with said capacitor means.
 3. The apparatus of claim 2 further comprising: voltage doubling means in series connection with said capacitor and differentiator means. 